Accurate analysis of the components of body composition can lay the ground work for the comprehension and prevention of various disease processes; however valid and accurate data are lacking for children, especially by the more accurate 4-component model. We will define the nutritional (energy and nutrient intake, total, resting, and physical activity energy expenditure), growth hormone, gonadal, and adrenal steroid hormone changes during childhood and adolescence that drive the alterations in body composition and regional fat distribution.